The present invention relates to a new and improved construction of a heat protective enclosure for an electronic device.
The present invention also relates to a new and improved construction of a heat protected electronic device.
More specifically, the present invention relates to a new and inventive construction of a heat protective enclosure as well as an electronic device protected by such enclosure against the action of high temperature such as produced on the exterior, for example, by a fire. In such arrangement, the electronic device is disposed within a housing which is surrounded by the heat protective enclosure.
Frequently there exists the necessity of maintaining full operability of the electronic device at least for a limited period of time even under the action of strong heat such as caused, for example, by an external fire. This is particularly true for critical security devices located in environments exposed to a fire hazard such as fuel storages or aircraft drive motors or engines. It is frequently impossible placing such electronic devices outside of the environment which is exposed to the fire hazard.
Protection from the action of strong heat possibly may be effected by heat insulation. For this purpose, insulating materials might be applied to an electronic device. The electronic device also might be disposed in an additional housing which is fire-protected.
A heat protected electronic device of the aforementioned type is known, for example, from British Published Patent Application No. 2,151,410A, published on Jul. 17, 1985, and is used in connection with the flight data memory unit of an aircraft. Therein, a mechanically resistant protective shell is provided with an internal liner made of a material which has a high melting point and low thermal conductivity. Printed circuit boards supporting solid-state memory devices are arranged within the liner and are preferably surrounded by a further shell. The high-temperature melting material of low thermal conductivity melts only at temperatures of about 1100.degree. C. and maintains the flight data memory unit at a temperature below or up to about 200.degree. C. for more than 4 hours even under the action of a fire.
This known heat protected electronic device permits heat insulation against the action of strong heat from the exterior. Many electronic devices, however, generate heat loss to an extent such that removal of the thus produced heat becomes indispensable. Preventing the heat removal by means of insulating material or a fire protective housing, will induce the risk of self-overheating of the electronic device. Moreover, a fire protective housing may be accompanied by an increase in space requirement and weight of the electronic device. This represents a serious disadvantage particularly in connection with the use thereof in an aircraft.
In order to remove the heat produced during normal operation of an electronic device, it is known, for example, from German Patent Publication No. 1,135,065, published on Aug. 23, 1962, to connect the chassis of the electronic device to a housing which is provided with air passage openings in the bottom wall and in the side walls. The cross-sectional area of the passage openings in the bottom wall is controlled by means of a bimetal-controlled plate. In this manner there is generated a cooling air flow through the housing in adaptation to the heat generated by the electronic device itself. Also, it is known from German Utility Model No. 7,505,337, published on Aug. 14, 1975, to provide supports, into which printed circuit boards are inserted, with aeration slots at their upper and lower surfaces.